Wireless line usage status monitoring method and device

ABSTRACT

For monitoring a wireless line usage status more effectively, a mobile station extracts a synchronizing signal of each of frames received from a plurality of base stations and a known signal transmitted together with transmission data within a time slot in which the transmission data are included but not transmitted within a time slot in which the transmission data are not included. The mobile station then measures a reception power of the synchronizing signal and a reception power of the known signal for each base station. And the mobile station determines a usage status of a wireless line of each base station based on the reception power of the synchronizing signal and the reception power of the known signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. application Ser.No. 12/691,839 filed on Jan. 22, 2010, this application is incorporatedby reference in its entirety for all purposes.

U.S. application Ser. No. 12/691,839 filed on Jan. 22, 2010 is acontinuation of International Application PCT/JP2007/65082 filed on Aug.1, 2007, the contents of which are herein wholly incorporated byreference.

FIELD

The present invention relates to a wireless line or channel (radio linkor channel) usage status monitoring method and device in a mobilecommunication system.

BACKGROUND

FIG. 13 illustrates an arrangement of a mobile communication systemgenerally known in the art. This mobile communication system 1 iscomposed of a mobile station 10, base stations 20_1-20 _(—) n(hereinafter, occasionally represented by a base station 20)respectively communicating with the mobile station 10 through wirelesslines RL1-RLn (hereinafter, occasionally represented by a wireless lineRL) and network connecting devices 30_1-30 _(—) m connected to the basestations 20 with a wired line WL to relay signals between the basestations 20 and a communication network NW.

It is to be noted that in order to effectively use the wireless line RLwith a restricted frequency band or the like, there is a method by whichthe mobile station 10 or the base stations 20 monitor a wireless lineusage rate (using or use rate) indicating a usage status of the wirelesslines.

Related art examples [1] and [2] for the monitoring technology will nowbe described referring to FIGS. 14-17:

Related Art Example [1] FIGS. 14-16

The related art mobile station 10 depicted in FIG. 14 includes atransmitting/receiving portion 11 for transmitting/receiving a frame FR(including data signal and various kinds of control signals) to/from thewireless line RL provided by the base stations 20 through an antennaANT, a measuring portion 12 for measuring a reception signal quality RQof the wireless line RL based on a specified signal within the frame FRand a control portion 13 for controlling and signal processing with thetransmitting/receiving portion 11 and the measuring portion 12.

The related art base stations 20 depicted in FIG. 15 includes atransmitting/receiving portion 21 for transmitting/receiving the frameFR to/from the mobile station 10 through the antenna ANT, a wired linejoint portion 22 connected to a wired line WL to transmit/receive thenumber of mobile stations during a call connection (hereinafter,occasionally referred to as a call connection number) NUM to/from otherbase stations and a control portion 23 for controlling and signalprocessing with the transmitting/receiving portion 21 and the wired linejoint portion 22.

In operation, each control portion 23 within the base stations 20_1-20_(—) n depicted in FIG. 16 periodically collects a call connectionnumber of each of the base stations 20_1-20 _(—) n through each wiredline joint portion 22 and calculates wireless line usage rates UR1-URn(hereinafter, occasionally represented by a usage rate UR) of the basestations 20_1-20 _(—) n based on the call connection number, whereby thewireless usage rates UR1-URn are to be shared between the base stations20_1-20 _(—) n (step T1). It is to be noted that there is also a casewhere the base stations 20_1-20 _(—) n measure a frame transmissionamount within the wireless line RL, an average transmission rate of thewireless line RL or the like, base on which the wireless line usage rateUR is calculated.

Meanwhile, there occurs a potential event where as the wireless lineusage rate UR increases, the base stations can not accept a call requestor a handover request from the mobile station and the transmission rateper mobile station is deteriorated in case of a communication system inwhich the wireless line is shared between a plurality of mobilestations.

For this event, assuming that the mobile station 10 is call connected tothe base station 20_1 as depicted by dotted lines in FIG. 16, thecontrol portion 23 within the base station 20_1 informs the mobilestation 10 of the wireless line usage rates UR1-URn through thetransmitting/receiving portion 21, thereby promoting implementation of ahandover based on the wireless line usage rates UR1-URn (step T2).

Upon receiving the wireless line usage rates UR1-URn, the measuringportion 12 in the mobile station 10 measures the reception signalqualities RQ1-RQn of the wireless lines of the base stations 20_1-20_(—) n to be provided to the control portion 13 (step T3).

The control portion 13 determines whether or not a handover to the basestations 20_2-20 _(—) n is implementable based on the reception signalquality RQ1 of the base station 20_1 during the call connection and thereception signal qualities RQ2-RQn of the adjacent base stations 20_2-20_(—) n (step T4).

Then the control portion 13 compares the wireless line usage rates ofthe base stations in which the handover is determined to beimplementable and determines a base station, with the lowest wirelessline usage rate, destined to be handed over, that is a handoverdestination base station (step T5).

Now assuming that the wireless line usage rate UR2 be the lowest, thecontrol portion 13 determines to implement the handover to the basestation 20_2 and notifies the handover request REQ to the base station20_1 through the transmitting/receiving portion 11 (step T6).

Having received the handover request REQ, the base station 20_1 providesa handover command CMD to the mobile station 10 to grant the handover tothe base station 20_2 (step T7), whereby the mobile station 10 is tohave a call connection with the base station 20_2 as depicted by dot anddash lines in FIG. 16.

In this way, the mobile stations are call connected to the base stationswith lower wireless line usage rates in a dispersed fashion, therebypreventing the wireless line usage rates from being increased (see e.g.Japanese Laid-open Patent Publication No. 2005-229417).

Also, as indicated in the following related art example [2], there is amethod of determining a handover destination of a mobile station mainlyled by a base station.

Related Art Example [2] FIG. 17

As depicted in FIG. 17, the base stations 20_1-20 _(—) n share thewireless line usage rates UR1-URn as with the above related art example[1] (step T1). At this time, the base station 20_1 during the callconnection with the mobile station 10 compares the wireless line usagerates UR1-URn, whereby the mobile station 10 determines a base stationto be handed over (or base station candidate destined to be handedover), different from the above related art example [1] (step T8).

Now assuming that the adjacent base station 20_2 be determined to behanded over, the base station 20_1 provides a measurement instruction ofreception signal quality INS2 to the mobile station 10 to measure thewireless line reception signal quality RQ1 of the base station 20_1itself and the wireless line reception signal quality RQ2 of the basestation 20_2 (step T9). It is to be noted that when the base stations asa handover candidate are determined at the above step T8, the basestation 20_1 instructs the mobile station 10 to measure the wirelessline reception signal quality of each base station as a handovercandidate.

The mobile station 10 having received the reception signal qualitymeasurement instruction INS2 measures the reception signal qualities RQ1and RQ2 (step T10) and notifies the measurement results to the basestation 20_1 (step T11).

When the base station determines that the mobile station 10 canimplement the handover to the base station 20_2 (step T12), the basestation 20_1 provides the handover command CMD to the mobile station 10to be forcibly handed over to the base station 20_2 (step T13), wherebythe mobile station 10 is to have a call connection with the base station20_2 as depicted by dot and dash lines in FIG. 17.

This case can also prevent the wireless line usage rate from beingincreased as with the above related art example [1].

It is to be noted that as a reference example, there is a mobilecommunication system in which a base station notifies a mobile stationof a reception signal power and a reception signal quality measured foran uplink electric wave and a transmission signal power of a downlinkelectric wave, so that the mobile station manages in an integratedfashion the state of the uplink electric wave and the state of thedownlink electric wave based on the reception signal power, receptionsignal quality and transmission signal power notified as well as areception signal power and a reception signal quality measured for thedownlink electric wave to carry out a handover control, thereby reducingthe loads of the base stations (see e.g. Japanese Laid-open PatentPublication No. 9-107573).

The above related art examples [1] and [2] have a problem that resourcesof wired lines are wasted since the wireless line usage rates are sharedthrough the wired lines connecting the base stations mutually, so thatparticularly such a waste is increased as the shared wireless line usagerates are updated in a shorter term.

Also the above related art example [1] has a problem that since thewireless line usage rates are required to be notified from the basestations during the call connection in order to make the mobile stationsdetermine the base stations to be handed over, so that this notificationitself causes an increase of the wireless line usage rate in whichparticularly such an increase is enlarged as the number of the adjacentbase stations increases.

SUMMARY

-   [1] According to an aspect of the invention, a wireless line usage    status monitoring method (or device) includes: extracting (or an    extracting portion extracting) a synchronizing signal of each of    frames received from a plurality of base stations and a known signal    transmitted together with transmission data within a time slot in    which the transmission data are included but not transmitted within    a time slot in which the transmission data are not included;    measuring (or a measuring portion measuring) a reception power of    the synchronizing signal and a reception power of the known signal    for each base station; and determining (or a determining portion    determining) a usage status of a wireless line of each base station    based on the reception power of the synchronizing signal and the    reception power of the known signal.

It is to be noted that the reception power of the above known signal maybe replace by a reception power of a time slot in case where the basestations transmit time slots (including data signal and the knownsignal) with a fixed power so that the mobile station can identify thereception power for each base station without using the known signal.

-   [2] In the above [1], the reception power of the known signal may    include an average reception power or a total reception power within    a single frame.-   [3] Also, in the above [1], the extracting (or the extracting    portion) may include: measuring (or a measuring portion measuring) a    reception signal quality of a wireless line of each base station;    determining (or a determining portion determining) handover    destination candidate base stations based on the reception signal    quality; and extracting (or an extracting portion extracting) the    synchronizing signal and the known signal of the frames only from    the handover destination candidate base stations and a base station    during a call connection.-   [4] Also, in the above [1], the determining (or the determining    portion) may include calculating (or a calculating portion    calculating) a wireless line usage rate as indicating the usage    status from a ratio of the reception power of the synchronizing    signal to the reception power of the known signal; and the method    (or the device) may further include selecting (or a selecting    portion selecting) a base station with the wireless line usage rate    being lowest as a handover destination base station.-   [5] In the above [4], the selecting (or the selecting portion) may    select, as the handover destination base station, a base station    with the wireless line usage rate being lowest and lower than a    specified value or a base station with the wireless line usage rate    being lowest and with a wireless line usage rate difference with    respect to a base station during a call connection exceeding a    specified threshold value.-   [6] Also, in the above [1], the method (or the device) may further    include measuring (or a measuring portion measuring) a wireless line    reception signal quality for each base station; calculating (or a    calculating portion calculating) an effective transmission rate of    each wireless line from the reception signal quality and the usage    status; and selecting (or a selecting portion selecting) the base    station with the effective transmission rate being highest as a    handover destination base station.-   [7] In the above [6], the selecting may select, as the handover    destination base station, a base station with the effective    transmission rate being highest and exceeding a specified threshold    value or a base station with the effective transmission rate being    highest and with an effective transmission rate difference with    respect to a base station during a call connection exceeding a    specified threshold value.-   [8] According to a further aspect of the invention, a wireless line    usage status monitoring method may include: extracting, when frames    are concurrently received from a plurality of base stations, a    synchronizing signal of a frame received from one base station and a    known signal transmitted together with transmission data within a    time slot in which the transmission data are included but not    transmitted within a time slot in which the transmission data are    not included; measuring a reception power of the synchronizing    signal and a reception power of the known signal for each base    station as well as an interference power with respect to the    synchronizing signal and an interference power with respect to the    known signal; first determining a wireless line usage status of the    one base station based on the reception power of the synchronizing    signal and the reception power of the known signal; and second    determining a wireless line usage status of a second base station    based on the interference power with respect to the synchronizing    signal and the interference power with respect to the known signal.-   [9] In the above [8], if the second base station includes a    plurality of base stations, the second determining may include    calculating a total wireless line usage rate of the second base    station as indicating the wireless line usage status of the second    base station from a ratio of the interference power of the    synchronizing signal to the interference power of the known signal.-   [10] Also, in the above [8], the reception power of the known signal    may include an average reception power or a total reception power    within a single frame and the interference power with respect to the    known signal may include an average interference power or a total    interference power within a single frame.-   [11] Also, in the above [8], the extracting may include: measuring a    wireless line reception signal quality of the second base station;    determining handover destination candidate base stations based on    the reception signal quality; and extracting the synchronizing    signal and the known signal only in presence of the handover    destination candidate base stations.-   [12] Also, in the above [8], the first determining may include    calculating a wireless line usage rate of the one base station as    indicating the wireless line usage status of the one base station    from a ratio of the reception power of the synchronizing signal to    the reception power of the known signal, and the second determining    may include calculating a wireless line usage rate of the second    base station as indicating the wireless line usage status of the    second base station from a ratio of the interference power with    respect to the synchronizing signal to the interference power with    respect to the known signal; and the method may further include    third measuring a wireless line reception signal quality of the    second base station when the wireless line usage rate of the second    base station is lower than the wireless line usage rate of the one    base station; and selecting a base station with a best usage rate as    a handover destination base station.-   [13] Also, in the above [12], the third measuring may measure the    reception signal quality when the wireless line usage rate of the    second base station is lower than the wireless line usage rate of    the one base station and a difference between the usage rates    exceeds a specified threshold value.

The object and advantages of the embodiment will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram depicting an arrangement of an embodiment [1]of a wireless line usage status monitoring method and device;

FIG. 2 is a sequence diagram depicting an operation of an embodiment [1]of a wireless line usage status monitoring method and device;

FIG. 3 is a flowchart depicting a handover implementabilitydetermination process in an embodiment [1] of a wireless line usagestatus monitoring method and device;

FIGS. 4A and 4B are block diagrams depicting a reception power measuringoperation in an embodiment [1] of a wireless line usage statusmonitoring method and device;

FIG. 5 is a block diagram depicting a reception power variationcharacteristic depending on a distance between a mobile station-basestation used in an embodiment [1] of a wireless line usage statusmonitoring method and device;

FIG. 6 is a flowchart depicting a line usage rate dispersion process inan embodiment [1] of a wireless line usage status monitoring method anddevice;

FIG. 7 is a block diagram depicting an arrangement of a modificationexample (1) of the embodiment [1];

FIG. 8 is a sequence diagram depicting an operation of a modificationexample (1) of the embodiment [1];

FIG. 9 is a flowchart depicting a line usage rate dispersion processexample in a modification example (1) of the embodiment [1];

FIG. 10 is a sequence diagram depicting an operation of a modificationexample (2) of the embodiment [1];

FIG. 11 is a sequence diagram depicting an operation of a modificationexample (3) of the embodiment [1];

FIG. 12 is a block diagram depicting an arrangement of an embodiment [2]of a wireless line usage status monitoring method and device;

FIG. 13 is a block diagram depicting a general arrangement of a mobilecommunication system;

FIG. 14 is a block diagram depicting an arrangement of a related artmobile station;

FIG. 15 is a block diagram depicting an arrangement of a related artbase station;

FIG. 16 is a sequence diagram depicting a related art example [1] with awireless line usage status monitoring technology; and

FIG. 17 is a sequence diagram depicting a related art [2] with awireless line usage status monitoring technology.

DESCRIPTION OF EMBODIMENTS

Embodiments [1] and [2] of a wireless line usage status monitoringmethod and device will now be described referring to FIGS. 1-12.

Embodiment [1] FIGS. 1-11

Arrangement: FIG. 1

The mobile station 10 according to this embodiment [1] as depicted inFIG. 1 replaces the measuring portion 12 in the related art exampledepicted in FIG. 14 with a measuring portion 12 a for measuring areception power RP_(S) of a synchronizing signal SS and an averagereception power RP_(AVG) of propagation path-estimating assistantsignals AS in a frame FR in accordance with a power measurementinstruction INS1 from the control portion 13 in addition to thereception signal quality RQ, and is further added with a line usage ratecalculator 14 for calculating a wireless line usage rate UR asindicating a usage status of the wireless line RL from both of thepowers RP_(S) and RP_(AVG).

It is to be noted that the above noted synchronizing signal SS ispositioned at the beginning of the TDMA (Time Division Multiple Access)frame and transmitted with a fixed power and a known pattern from thebase station, serving to synchronize the base station with the mobilestation.

And the above noted propagation path-estimating assistant signals AS iscontained within a time slot of the frame as the aforementioned knownsignal, transmitted with a fixed power and a known pattern from the basestation and is used by the mobile station for performing compensationsof amplitude and phase as well as error corrections or the like withrespect to data signal (not depicted) within the frame.

It is to be noted that the above time slot may be occupied by a singlemobile station or shared with a plurality of mobile stations.

Operation Example FIGS. 2-6

As depicted in FIG. 2, the transmitting/receiving portion 11 forming themobile station 10 provides frames FR1-FRn respectively received from thebase stations 20_1-20 _(—) n in the mobile communication system to themeasuring portion 12 a (step S1), where the frame FR is also provided tothe control portion 13 while the description is omitted, so that avarious kinds of communication processings are executed according to thecontents of the data signal or the control signal within the frame FR.

As with the measuring portion 12 depicted in FIG. 14, the measuringportion 12 a measures the reception signal qualities RQ1-RQn of thewireless lines of the base stations 20_1-20 _(—) n respectively from theframes FR1-FRn to be provided to the control portion 13 (step S2).

The control portion 13 executes a handover implementabilitydetermination processing based on the reception signal qualities RQ1-RQn(step S3).

Namely, as depicted in FIG. 3, when the reception signal qualitiesRQ1-RQn are received (step 31), the control portion 13 compares in orderthe reception signal quality RQ1 of the base station 20_1 during thecall connection and the reception signal qualities RQ2-RQn of theadjacent base stations 20_2-20 _(—) n to determine whether or not ahandover to the base stations 20_2-20 _(—) n is implementable (stepS32).

It is to be noted that the control portion 13 may be adapted todetermine that the handover is implementable only if the receptionsignal qualities RQ2-RQn exceeds a specified threshold value or thedifference between the reception signal qualities RQ2-RQn and thereception signal quality RQ1 exceeds a specified threshold value.

At step S32, if the control portion 13 determines that the handover isunimplementable, the mobile station 10 will not perform the processingsat step S4 and the following steps depicted in FIG. 2 (step S33).

On the other hand, if the control portion determines that the handoveris implementable, the mobile station 10 determines the base station as abase station as a handover destination candidate (step S34).

Now assuming that only the base station 20_2 be determined as a handoverdestination candidate base station, the control portion 13 provides thepower measurement instruction INS1 to the measuring portion 12 a tomeasure the reception power RP_(S) of the synchronizing signal and theaverage reception power RP_(AVG) of the propagation path-estimatingassistant signals AS with regard to the frames FR1 and FR2 received fromthe base stations 20_1 and 20_2, respectively (step S4).

The measuring portion 12 a having received the power measurementinstruction INS1 measures a reception power RP_(S) 1 of thesynchronizing signal SS within the frame FR1 as depicted in FIG. 4A.Then the measuring portion 12 a measures an average reception power(reception power of the known signal) RP_(AVG) 1 of the propagationpath-estimating assistant signals AS included in the time slots TS0-TS7following the synchronizing signal SS.

In this case, all of the time slots TS0-TS7 are used for thetransmission of the data signal DS as depicted, so that the measuringportion 12 a measures reception powers RP_(A) 10-RP_(A) 17 of thepropagation path-estimating assistant signals AS and calculates theaverage reception power RP_(AVG) 1 from the reception powers RP_(A)10-RP_(A) 17 to be provided to the line usage rate calculator 14.

As depicted in FIG. 4B, the measuring portion 12 a measures a receptionpower RP_(S) 2 of the synchronizing signal SS and an average receptionpower RP_(AVG) 2 of the propagation path-estimating assistant signals ASwith respect to the frame FR2 as well in the same manner as the above,to be provided to the line usage rate calculator 14, where as depictedby oblique lines in FIG. 4B in the frame FR2 the time slots TS0, TS3,TS5 and TS6 are not used for the transmission of the data signal DS, sothat the average reception power RP_(AVG) 2 is measured as a value lowerthan the average reception power RP_(AVG) 1.

It is to be noted that the reception powers RP_(S) 1 and RP_(S) 2 varydepending on the distance between the mobile station 10-the base station20 regardless of the time slots TS0-TS7 being used/unused.

The line usage rate calculator 14 having received the average receptionpowers RP_(AVG) 1 and RP_(AVG) 2 calculates a wireless line usage rateUR1 of the base station 20_1 and a wireless line usage rate UR2 of thebase station 20_2 in accordance with the following Equations (1) and (2)(step S5):wireless line usage rate UR1=average reception power RP_(AVG)1/receptionpower RP_(S)1  Eq. (1)wireless line usage rate UR2=average reception power RP_(AVG)2/receptionpower RP_(S)2  Eq. (2)

The reason why the wireless line usage rate UR is calculated from theratio of the reception power RP_(S) of the synchronizing signal to theaverage reception power RP_(AVG) of the propagation path-estimatingassistant signals AS is that as depicted in FIG. 5 even though both ofthe powers RP_(S) and RP_(AVG) vary depending on the distance L betweenthe mobile station 10-base station 20, the wireless line usage rate URcan be obtained as a unique value.

Namely, a reception power RP_(S) _(—) L2 and an average reception powerRP_(AVG) _(—) L2 at the time when the distance L=“L2 (>L1)” respectivelybecome lower than a reception power RP_(S) _(—) L1 and an averagereception power RP_(AVG) _(—) L1 at the time when the distance L=“L1”,where the ratio of the average reception value RP_(AVG) _(—) L1 to thereception power RP_(S) _(—) L1 is equal to the ratio of the averagereception power RP_(AVG) _(—) L2 to the reception power RP_(S) _(—) L2.Therefore, the wireless line usage rate UR calculated at the above stepS5 does not depend on the distance L between the mobile station 10-thebase station 20.

It is to be noted that upon calculating the wireless line usage rate UR,a total reception power of the propagation path-estimating assistantsignals AS may be substituted for the average reception power RP_(AVG).In this case as well, a unique wireless line usage rate UR independentof the distance L between the mobile station 10-the base station 20 canbe obtained.

Then the control portion 13 executes a line usage rate dispersionprocessing based on the wireless line usage rates UR1 and UR2 (step S6).

Namely, as depicted in FIG. 6, when having received the wireless lineusage rates UR1 and UR2 (step S61), the control portion 13 determineswhether or not the wireless line usage rate UR2 is lower than thewireless line usage rate UR1 (step S62).

Now assuming that “wireless line usage rate UR2<wireless line usage rateUR1” is established, the control portion 13 selects the base station20_2 as a handover destination (step S63), where in the presence of aplurality of base stations of which wireless line usage rate is lowerthan the base station 20_1, the control portion 13 selects a basestation of which wireless line usage rate is the lowest.

Meanwhile, at the above step S63, the control portion 13 may be adaptedto select the base station 20_2 as a handover destination only if thewireless line usage rate UR2 is below a specified threshold value (notdepicted) or the deference between the wireless line usage rate UR2 andthe wireless line usage rate UR1 exceeds a specified threshold value(namely if the dispersion effect of the line usage rate is sufficientlyachieved due to the handover to the base station 20_2).

On the other hand, if it is found by the determination at the above stepS62 that there is no base station with the wireless line usage ratebeing lower than the base station 20_1, the control portion 13 executesno handover operation (step S64).

Then, the control portion 13 notifies a handover request REQ to the basestation 20_1 during the call connection as depicted in FIG. 2 (step S7).

The base station 20_1 having received the handover request REQ notifiesthe mobile station 10 of the handover command CMD and permits thehandover to the base station 20_2 (step S8), whereby the mobile station10 is to be call connected to the base station 20_2 as depicted by dotand dash lines in FIG. 2.

Thus, without performing steps T1 and T2 depicted in FIG. 16 as arelated art example (share of wireless line usage rates between the basestations and notification of wireless line usage rate to the mobilestation), the wireless line usage status can be monitored.

Hereinafter, modification examples (1)-(3) will now be describedreferring to FIGS. 7-11.

Modification Example (1) FIGS. 7-9

The mobile station 10 depicted in FIG. 7 is provided, in addition to thearrangement depicted in FIG. 1, with a transmission rate calculator 15for calculating an effective transmission rate ER of the wireless lineRL based on the reception signal quality RQ and the wireless line usagerate UR respectively outputted from the measuring portion 12 a and theline usage rate calculator 14.

FIG. 8 depicts an operation of the mobile station 10 in thismodification example, where step S9 is newly added to the operationsequence depicted in FIG. 2, corresponding to which a line usage ratedispersion processing (step S6 a) based on the effective transmissionrate ER is substituted for the processing of step S6.

Namely, when the wireless line usage rate UR1 of the base station 20_1and the wireless line usage rate UR2 of the base station 20_2 arecalculated in the same manner as the above embodiment [1], thetransmission rate calculator 15 calculates the wireless line effectivetransmission rate ER1 of the base station 20_1 from the wireless lineusage rate UR1 and the reception signal quality RQ1 and calculates thewireless line effective transmission rate ER2 of the base station 20_2from the wireless line usage rate UR2 and the reception signal qualityRQ2, the effective transmission rates ER1 and ER2 being provided to thecontrol portion 13 (step S9), as follows:effective transmission rate ER1=maximum transmission rateMR1*(1-wireless usage rate UR1)  Eq. (3)effective transmission rate ER2=maximum transmission rateMR2*(1-wireless usage rate UR2)  Eq. (4)where the maximum transmission rates MR1 and MR2 of the above Equations(3) and (4) (hereinafter, occasionally represented by the maximumtransmission rate MR) respectively correspond to the transmission ratesat the time when the wireless line usage rates UR1 and UR2 are both “0”.In case of an adaptive modulation system, this maximum transmission rateMR can be uniquely calculated (specified) from the reception signalquality RQ.

Also, “1-wireless line usage rate UR1” and “1-wireless line usage rateUR2” in the above Equations (3) and (4) respectively correspond to thewireless line usage rates of the base stations 20_1-20_2 (rate of themobile station 10 capable of using the wireless line).

Then the control portion 13 executes the line usage rate dispersionprocessing based on the effective transmission rates ER1 and ER2 (stepS6 a).

Namely, as depicted in FIG. 9, when having received the effectivetransmission rates ER1 and ER2 (step S61 a), the control portion 13determines whether or not the effective transmission rate ER2 is largerthan the effective transmission rate ER1 (step S62 a).

Now assuming that “the effective transmission rate ER2>the effectivetransmission rate ER1” be established, the control portion 13 selectsthe base station 20_2 as a handover destination (step S63 a), where inthe presence of a plurality of base stations with the effectivetransmission rate being larger than the base station 20_1, the controlportion 13 selects the base station with the highest effectivetransmission rate as a handover destination.

Also in the above step S63 a, the control portion 13 may be adapted toselect the base station 20_2 as a handover destination only if theeffective transmission rate ER2 exceeds a specified threshold level (notdepicted) or the difference between the effective transmission rate ER2and the effective transmission rate ER1 exceeds a specified thresholdlevel (i.e. if the effective transmission rate ER2 sufficiently meets atransmission rate desired by the mobile station 10).

On the other hand, if it is found from the determination at the abovestep S62 a that there exists no base station with the effectivetransmission rate being higher than the base station 20_1, the controlportion 13 executes no handover operation (step S64 a).

Hereinafter, by a mutual operation between the mobile station 10 and thebase station 20_1 (steps S7 and S8 in FIG. 8), the mobile station 10 isto be call connected to the base station 20_2 as with the aboveembodiment [1].

Modification Example [2] FIG. 10

FIG. 10 depicts a mutual operation between the mobile station 10 and thebase station 20 in this modification example, in which the proceedingsat steps S3, S5 and S6 in the operation sequence depicted in FIG. 2 aremodified so as to be executed on the side of the base station 20, sothat the handover destination of the mobile station 10 can be determinedmainly led by the base station. In this case, it is necessary to provideblocks similar to the control portion 13 and the line usage ratecalculator 14 depicted in FIG. 1 in the base station 20.

In operation, the mobile station 10 notifies the reception signalqualities RQ1-RQn, the reception powers RP_(S) 1-RP_(S)n of thesynchronizing signals within the frames FR1-FRn and the averagereception powers RP_(AVG) 1-RP_(AVG)n of the propagation path-estimatingassistant signals measured as with the above embodiment [1] to the basestation 20_1 during the call connection (step S10).

Assuming that the base station 20_2 is selected as a handoverdestination as with the above embodiment [1] as a result that the basestation 20_1 has executed the processings of steps S3, S5 and S6, thebase station 20_1 gives the handover command to the mobile station 10 tobe forcibly handed over to the base station 20_2 (step S8).

Modification Example (3) FIG. 11

FIG. 11 depicts a mutual operation between the mobile station 10 and thebase station 20, which is, as depicted, modified to execute theprocessings of steps S3, S5, S9 and S6 a in the operation sequencedepicted in FIG. 8 on the side of the base station 20, so that thehandover destination of the mobile station 10 can be determined mainlyled by the base station based on the effective transmission rate ER.

In this case, it is necessary to provide blocks similar to the controlportion 13, the wire usage rate calculator 14 and the transmission ratecalculator 15 depicted in FIG. 7 in the base station 20.

Embodiment [2]: FIG. 12

The mobile station 10 according to this embodiment [2] depicted in FIG.12 employs a measuring portion 12 b for measuring an interference powerIP_(S) with respect to the synchronizing signal SS and an averageinterference power IP_(AVG) with respect to the propagationpath-estimating assistant signals AS in addition to the reception signalquality RQ as well as the reception power RP_(S) of the synchronizingsignal SS and the average reception power RP_(AVG) of the propagationpath-estimating assistant signals AS within the frame FR and a lineusage rate calculator 14 b for calculating a wireless line usage rate URindicating a usage status of the wireless line RL from those powersRP_(S), RP_(AVG), IP_(S) and IP_(AVG), instead of the measuring portion12 a and the line usage rate calculator 14 in the above embodiment [1],respectively.

Hereinafter, an operation of this embodiment will be described by takingas an example a case where the frames FR1-FRn are concurrently receivedfrom the base stations 20_1-20 _(—) n depicted in FIG. 2.

First, the control portion 13 executes the same handoverimplementability determination processing as the above embodiment [1]based on the wireless line reception signal qualities RQ1-RQn of thebase stations 20_1-20 _(—) n. As a result, only when the base station asa handover candidate is determined, the control portion 13 provides thepower measurement instruction INS1 to the measuring portion 12 b tomeasure e.g. the reception power RP_(S) of the synchronizing signal SSand the average reception power RP_(AVG) of the propagationpath-estimating assistant signals AS within the frame FR1 as well as theinterference power IP_(S) to the synchronizing signal AS and the averageinterference power IP_(AVG) to the propagation path-estimating assistantsignals AS.

It is to be noted that the above interference power IP_(S) and theaverage interference power IP_(AVG) respectively correspond to a totalreception power of the synchronizing signals and a total of the averagereception powers of the propagation path-estimating assistant signalswithin the frames FR2-FRn.

While calculating the wireless line usage rate UR1 of the base station20_1 from the reception power RP_(S) and the average reception powerRP_(AVG) in accordance with the above Equation (1), the line usage ratecalculator 14 b calculates a total wireless line usage rate UR_(SUM) ofthe other base stations 20_2-20 _(—) n from the interference powerIP_(S) and the average interference power IP_(AVG) in accordance withthe following Equation (5):total wireless line usage rate UR_(SUM)=average interference powerIP_(AVG)/interference power IP_(S)  Eq. (5)

Now assuming that “total wireless line usage rate UR_(SUM)<wireless lineusage rate UR1” be established, the control portion 13 determines toimplement the handover to any of the base stations as the handovercandidates. It is to be noted that the control portion 13 may be adaptedto determine the handover implementation only if the total wireless lineusage rate UR_(SUM) is below a specified threshold value or thedifference between the total wireless line usage rate UR_(SUM) and thewireless line usage rate UR1 exceeds a specified threshold value(namely, if a dispersion effect of the wireless line usage rate can besufficiently achieved by the handover).

Then the control portion 13 selects the base station with the bestreception signal quality RQ from among the base station candidates to behanded over as a handover destination.

Thus, as with the above embodiment [1], it is possible to monitor thewireless line usage status without executing the processings of steps T1and T2 depicted in FIG. 16 (share of the wireless line usage ratesbetween the base stations and notification of the wireless line usagerate to the mobile station).

Also, since the synchronizing signal SS and the propagationpath-estimating assistant signals AS are not measured for each basestation, it is possible to shorten the calculation time for the wirelessline usage rates.

In case where the present invention is applied to an OFDMA (OrthogonalFrequency Division Multiple Access) mobile communication system, thetime slot may be replaced by a slot formed of time access and frequencyaccess, including the propagation path-estimating assistant signals aswell.

Also in the above modification examples (2) and (3), the mobile stationmay calculate the wireless line usage rate or the effective transmissionrate to be notified to the base station during the call connection.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A wireless line usage status monitoring methodcomprising: extracting a synchronizing signal of each of frames receivedfrom a plurality of base stations and a known signal of each of timeslots included in each of the frames, the known signal being transmittedtogether with transmission data within a time slot in which thetransmission data is included but not being transmitted within a timeslot in which the transmission data is not included; measuring areception power of the synchronizing signal and a reception power of theknown signal for each base station; and determining a usage status of awireless line of each base station based on the reception power of thesynchronizing signal and an average reception power or a total receptionpower over the reception powers of the known signals transmitted in theframe.
 2. The wireless line usage status monitoring method as claimed inclaim 1, wherein the extracting comprises: measuring a reception signalquality of a wireless line of each base station; determining handoverdestination candidate base stations based on the reception signalquality; and extracting the synchronizing signal and the known signal ofthe frames only from the handover destination candidate base stationsand a base station during a call connection.
 3. The wireless line usagestatus monitoring method as claimed in claim 1, wherein the determiningcomprises calculating a wireless line usage rate as indicating the usagestatus from a ratio of the reception power of the synchronizing signalto the reception power of the known signal; the method furthercomprising selecting a base station with the wireless line usage ratebeing lowest as a handover destination base station.
 4. The wirelessline usage status monitoring method as claimed in claim 1, furthercomprising measuring a wireless line reception signal quality for eachbase station; calculating an effective transmission rate of eachwireless line from the reception signal quality and the usage status;and selecting the base station with the effective transmission ratebeing highest as a handover destination base station.
 5. A wireless lineusage status monitoring method comprising: extracting, when frames areconcurrently received from a plurality of base stations, a synchronizingsignal of a frame received from one base station and a known signal ofeach of time slots included in the frame, the known signal beingtransmitted together with transmission data within a time slot in whichthe transmission data is included but not being transmitted within atime slot in which the transmission data is not included; measuring areception power of the synchronizing signal and a reception power of theknown signal for each base station as well as an interference power withrespect to the synchronizing signal and an interference power withrespect to the known signal; first determining a wireless line usagestatus of the one base station based on the reception power of thesynchronizing signal and an average reception power or a total receptionpower over the reception powers of the known signals transmitted in theframe; and second determining a wireless line usage status of a secondbase station based on the interference power with respect to thesynchronizing signal and the interference power with respect to theknown signal.
 6. The wireless line usage status monitoring method asclaimed in claim 5, wherein if the second base station includes aplurality of base stations, the second determining comprises calculatinga total wireless line usage rate of the second base station asindicating the wireless line usage status of the second base stationfrom a ratio of the interference power of the synchronizing signal tothe interference power of the known signal.
 7. The wireless line usagestatus monitoring method as claimed in claim 5, wherein the interferencepower with respect to the known signal is an average interference poweror a total interference power within a single frame.
 8. The wirelessline usage status monitoring method as claimed in claim 5, whereintheextracting comprises: measuring a wireless line reception signalquality of the second base station; determining handover destinationcandidate base stations based on the reception signal quality; andextracting the synchronizing signal and the known signal only inpresence of the handover destination candidate base stations.
 9. Awireless line usage status monitoring method comprising: extracting asynchronizing signal of each of frames received from a plurality of basestations and time slots, in each of which transmission data is included,included in each of the frames; measuring a reception power of thesynchronizing signal and a reception powers of the time slots for eachbase station; and determining a usage status of a wireless line of eachbase station based on the reception power of the synchronizing signaland an average reception power or a total reception power over thereception powers of the time slots transmitted in the frame.
 10. Awireless line usage status monitoring device comprising: an extractingportion to extract a synchronizing signal of each of frames receivedfrom a plurality of base stations and a known signal of each of timeslots included in each of the frames, the known signal being transmittedtogether with transmission data within a time slot in which thetransmission data is included but not being transmitted within a timeslot in which the transmission data is not included; a measuring portionto measure a reception power of the synchronizing signal and a receptionpower of the known signal for each base station; and a determiningportion to determine a usage status of a wireless line of each basestation based on the reception power of the synchronizing signal and anaverage reception power or a total reception power over the receptionpowers of the known signals transmitted in the frame.
 11. The wirelessline usage status monitoring device as claimed in claim 10, wherein theextracting portion comprises: a measuring portion to measure a receptionsignal quality of a wireless line of each base station; a determiningportion to determine handover destination candidate base stations basedon the reception signal quality; and an extracting portion to extractthe synchronizing signal and the known signal of the frames only fromthe handover destination candidate base stations and a base stationduring a call connection.
 12. The wireless line usage status monitoringdevice as claimed in claim 10, wherein the determining portion comprisesa calculating portion to calculate a wireless line usage rate asindicating the usage status from a ratio of the reception power of thesynchronizing signal to the reception power of the known signal; thedevice further comprising a selecting portion to select a base stationwith the wireless line usage rate being lowest as a handover destinationbase station.
 13. The wireless line usage status monitoring device asclaimed in claim 10, further comprising a measuring portion to measure awireless line reception signal quality for each base station; acalculating portion calculating an effective transmission rate of eachwireless line from the reception signal quality and the usage status;and a selecting portion to select the base station with the effectivetransmission rate being highest as a handover destination base station.